1. Field of the Invention
The present invention relates to an image pickup optical system and an image pickup apparatus using the same.
2. Description of the Related Art
With the recent demand for thinner cellular phones, personal digital assistants, or notebook computers, camera modules are required to make the length of the image pickup optical system in the optical axis direction thinner to the utmost limit. To meet this requirement, there are proposed many single-focus image pickup optical systems including about two to four aspheric lenses.
Further, with the recent technological advances in and growing market needs for image pickup devices, high-resolution image pickup devices are used, and this requires high-resolution lenses. However, even using conventional lenses having an F-number of about F3.2 or F2.8, it has become difficult to obtain sufficient performance because of the effects of diffraction. As image pickup optical systems in which the entire optical length is reduced while reducing F-number to 2.8 or less to enhance the image formation performance, structures with five lenses are proposed, for example, in the following Japanese Patent Application Laid-Open No. 2009-294527 and Japanese Patent Application Laid-Open No. 2010-48996.